1. Field
The present invention relates generally to wireless communications, and more particularly, to a method and apparatus for sensing signaling parameters in a wireless communications network.
2. Background
Wireless communication networks such as the Forward Link Only (FLO) network have been designed to provide real-time audio and video multicasting to mobile devices. The FLO system is designed to work in a mobile environment where the channel characteristics in terms of the number of channel taps with significant energy, path gains and the path delays are expected to vary quite significantly over a period of time. To achieve good receiver performance and high spectral efficiency, the FLO network uses Orthogonal Frequency Division Multiplexing (OFDM) as the modulation technique. In the OFDM approach, the available bandwidth is divided into N bins, referred to as sub-carriers, with each sub-carrier modulated by a Quadrature Amplitude Modulated (QAM) symbol. The timing synchronization block in a receiver device responds to changes in the channel profile by selecting the OFDM symbol boundary appropriately to maximize the energy captured in the Fast Fourier Transform (FFT) window.
One important principle of OFDM is that a number of low-rate streams is transmitted in parallel instead of a single high-rate stream, because low symbol rate modulation schemes (i.e., schemes where the symbols are relatively long compared to the channel time characteristics) suffer less from interference caused by multipath. Since the duration of each symbol is long, it is feasible to insert a guard interval between the OFDM symbols to reduce the intersymbol interference. During the guard interval, a cyclic prefix, which consists of the end of the OFDM symbol, is transmitted with the OFDM symbol. The reason that the guard interval includes a copy of the end of the OFDM symbol is so that the receiver will integrate over an integer number of sinusoid cycles for each of the multipaths when it performs OFDM demodulation with FFT.
The signaling parameters (SP) of a particular FLO network, such as the FFT size as well as the guard interval, need to be determined by a wireless receiver device during the power-up or initialization process. Otherwise, the receiver cannot decode the waveforms of the FLO network if it does not know the proper SP. Further, FLO networks can support multiple combination of SPs (i.e., a combination of different FFT sizes and multiple cyclic prefix lengths, among other parameters), and a wireless communications system may have multiple FLO networks, with each FLO network being differently configured. In other words, each FLO network may have a different set of SPs, where each FLO network being configured for a different FFT size and/or cyclic prefix length.
One problem encountered when implementing a mobile receiver moving between FLO networks that have different SPs is that the correct values for them cannot be conveyed to a receiver inside the FLO waveform itself using existing means, since symbol demodulation requires that the receiver would have already picked the correct values for these parameters.